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Silicon Quantum Computation

The Precision Qubit Program led by Professor Simmons leads the field in making precision single dopant devices in silicon for both conventional and quantum computing. Using a combination of scanning tunneling microscopy and molecular beam epitaxy P dopant atoms are controllably placed in Si devices with atomic precision. This has led to the development of the narrowest conducting wires in silicon, the development of the smallest precision transistors and complex single atom architectures for spin qubits. The Program is currently developing all the functional elements for a practical and scalable spin-based quantum computer, including techniques for single-shot spin readout, coherent Rabi rotations, controlled exchange interactions and spin transport.

The goal of this program is to understand the physics of the qubit coupling with the environment to understand decoherence pathways and to control. The control over the electron wavefunction requires interfaces which lead to the loss of bulk properties of the qubit due to physical processes like the valley-orbit coupling, exchange, and many-body effects in coherent coupling. The atomistic understanding of the interaction between the environment and the qubit is essential for quantum computation since it allows the achievement of optimal coherence times and optimal robustness of the quantum gates. Optical addressing of electrons in Si is nontrivial but vastly beneficial due to the gained flexibility and unprecedented high resolution. We investigate efficient read-out and coupling schemes to open up new pathways into optical control.

The Integrated Silicon Nano-Spintronics program, led by Professor Andrew Dzurak, focuses on engineering design, modeling, nanofabrication and measurement of fully-configured Si:P spin qubits and associated pathway devices. The team makes extensive use of the Australian National Fabrication Facility (ANFF) at UNSW for device fabrication and maintains close links with leading international groups in silicon nanoelectronics and spintronics. The team’s development of a MOS-compatible Al-AlOx gate-stack technology has been critical to numerous recent experimental outcomes, including highly tunable Si quantum dot devices operating at the single electron limit, single-P-donor nano-FETs, and Si:P spin qubit devices with integrated Si SETs for single-shot spin readout.

An electronic or nuclear spin represents the quintessential quantum-mechanical two-level system. The Quantum Spin Control Program develops the methods to gain full quantum control of single spins in solid state. These include single-shot spin readout, coherent Rabi rotations, controlled exchange interactions, spin transport, and electron-nuclear entanglement. The group combines a strong background in quantum magnetism and spin resonance techniques with of state-of-the-art nanotechnology, and aims at demonstrating all the building blocks of a functional and scalable spin-based quantum computer.

Electron spins bound to phosphorus donors in silicon (Si:P qubits) are extremely attractive for large-scale quantum computing due to their extremely long coherence times (~1s) and the potential of scaling using industrial silicon manufacturing. Fabrication of devices that use single atoms as their functional elements presents formidable challenges. Our method, based on the implantation of single ions into silicon and detecting the induced charge, successfully meets this challenge. In close collaboration with our UNSW colleagues, we apply this method to the fabrication of quantum computer devices containing few or single atoms in which single electron spins can be controlled and read-out.